Mesh networking is a type of networking topology whereby each node in the network is able not only to capture data for its own purposes, but also act as a relay to forward data onwards to another node in the network. An example is ZigBee, which refers to a suite of protocols including ZigBee Light Link designed for mesh networking.
ZigBee Light Link (ZLL) is an open standard designed for LED lighting control. Components such as LED fixtures, sensors, timers, remotes and switches configured according to ZLL can connect into a network without a special device to coordinate this. As an example of a ZLL based system, Philips hue is a ZLL based lighting system containing a bridge controller and a number of lighting nodes (e.g. LED “bulbs”). The bridge device has the function of bridging between the ZigBee devices (e.g. lighting nodes) and one or more other devices such as IP devices (e.g. a smart phone or tablet), but it does not act as a centralized coordinator, at least not for the purpose of the ZLL networking protocol.
To make sure that consumers can easily install and add devices into their home lighting network, ZLL includes a commissioning mechanism which is simple for consumers and does not have a need for a coordinator. This mechanism is known as Touchlink. Taking the Philips hue system as an example, the basic steps of the Touchlink based network commissioning, i.e. the process of connecting the bridge controller and multiple other nodes such as light bulbs into a ZLL network, are as follows.
First, the user initiates the network creation process by invoking the “discover new bulbs” operation using a smart phone app.
Next, the bridge controller performs the device discovery procedure of the Touchlink commissioning process. As the initiator, the bridge controller broadcasts eight inter-PAN (inter personal area network) scan request command frames, spaced at a predefined interval, which is roughly 250 ms. Devices (e.g. the bulbs) receiving the scan request may choose whether to respond and, if so, the device shall unicast a scan response inter-PAN command frame back to the initiator. A device shall only respond to a received scan request if its RSSI (received signal strength indicator) is above a certain manufacture specific threshold, which determines the so-called Touchlink vicinity range of the initiator. In other words, only devices located within the range can be discovered by the initiator.
Then the bridge select one of the devices discovered in the above step and unicasts a network start request inter-PAN command frame to the selected device. On receipt of the request, the selected device shall start a new network and unicast a network start response inter-PAN command frame to the bridge indicating success.
For the rest of the discovered devices, the bridge shall unicast a network join router (or join end device) request inter-PAN command frame to each of these devices. On receipt of the request, the device shall join the network and unicast a network join router (or join end device) response inter-PAN command frame to the bridge indicating success.